The present invention relates to a pattern inspecting apparatus suitable for inspection of a pattern on a semiconductor wafer, liquid-crystal glass, or the like.
The inspection of the acceptability of a pattern formed on a semiconductor wafer is typically performed by using the following methods.
(a) The wafer is tilted at various angles while strong light is being applied to the wafer from a diagonal direction, and an inspector macroscopically inspects the wafer visually under dark-field observation. This macroscopic inspection is made by making use of the fact that the state of diffracted light from the pattern formed on the wafer subtly differs from the state of a non-defective unit.
(b) The wafer is macroscopically inspected by the inspector visually under bright-field observation by making use of diffused lighting which is larger than the wafer and by principally making use of regularly reflected light. This macroscopic inspection is also made by making use of the fact that the brightness and the color subtly differ from the state of a non-defective unit.
(c) The configuration of the pattern is microscopically inspected visually or automatically by using an optical microscope.
(d) The configuration of the pattern is inspected in detail in a pinpoint manner by using a scanning electron microscope.
However, according to the above-described inspection, the following problems have been encountered.
According to the methods (a) and (b), since inspection is performed visually by a human being, it is difficult to detect defects if the overall wafer surface is uniformly abnormal. In addition, the visual inspection by a human being can be performed at high speed, but there are variations in the inspection capability among inspectors and there are oversights, so that there is a drawback in ensuring stable and sufficient quality of inspection.
In the inspection (c) using the optical microscope, since it is a microscopic inspection, it takes excessive time in inspecting all the fine pattern. In addition, although line width of the pattern formed on the wafer has recently become very small, the inspection of a pattern which is finer than a limit of resolution in relation to the wavelength of light is virtually impossible with the optical microscope. Furthermore, in a case of inspection for a resist that passes light therethrough, since the configuration of the pattern cannot be observed clearly, inspection accuracy is poor.
In the inspection (d) using the scanning electron microscope, although measurement accuracy is high, since it is a pinpoint inspection, an enormously long time is required for inspecting an average line width and its distribution.
In view of the above-described background art, an object of the present invention is to provide an inspecting apparatus which is capable of macroscopically inspecting a step structure such as a fine pattern (the step referred to herein means a structure in which the phase of light reflected from or transmitted through this portion has a value different from the phase of the light of other portions) and of easily obtaining average information thereof.
To attain the above-described object, the present invention is characterized by comprising the following features.
(1) A pattern inspecting apparatus which inspects a pattern formed on a workpiece to be inspected, said apparatus comprising:
an illuminating optical system which illuminates a pattern in a region subject to inspection on a workpiece in a substantially perpendicular direction;
a detecting optical system which detects regularly reflected light or transmitted light from the pattern illuminated by the illuminating optical system, the detecting optical system having a numerical aperture which does not allow a structure of the pattern in the region subject to inspection to be optically resolved;
a wavelength-varying system which selectively renders variable a wavelength of the light to be detected by the detecting optical system; and
a measuring system which measures the structure of the pattern on the basis of light intensity information of the detected light in correspondence with the wavelength varied by the wavelength-varying system.
(2) The pattern inspecting apparatus as set forth in (1), wherein the wavelength-varying system is provided in the illuminating optical system to selectively vary a central wavelength to thereby provide illuminating light of a narrow band.
(3) The pattern inspecting apparatus as set forth in (1), wherein the illuminating optical system emits illuminating light of a wide band, and the wavelength-varying system is provided in the detecting optical system to selectively vary a central wavelength so that the detecting optical system detects light of a narrow band.
(4) The pattern inspecting apparatus as set forth in (1), wherein the light intensity information represents intensity characteristic of interfering light in relation to varied wavelength, the interfering light is caused by light from a pattern portion in the region subject to inspection and by light from the rest in the region subject to inspection, and the measuring system obtains an average characteristic parameter regarding the structure of the pattern on the basis of the intensity characteristic of interfering light.
(5) The pattern inspecting apparatus as set forth in (4), wherein the parameter relates to an average area ratio of the pattern portion in the region subject to inspection, an average area ratio of the rest in the region subject to inspection, or a line width of the pattern in the region subject to inspection.
(6) The pattern inspecting apparatus as set forth in (4), wherein the parameter is obtained on the basis of a periodicity of a changed waveform and an amplitude thereof in the intensity characteristic of interfering light obtained by varying the wave length.
(7) The pattern inspecting apparatus as set forth in (4), further comprising:
a storage device which stores therein standard intensity characteristics of interfering light obtained respectively from a non-defective workpiece and a defective workpiece;
wherein the parameter is obtained on the basis of a degree of similarity with respect to the standard intensity characteristic stored in the storage device.
(8) The pattern inspecting apparatus as set forth in (1), further comprising:
a storage device which stores therein a result of measurement on a standard workpiece;
a judging system which judges whether or not the pattern in the region subject to inspection is defective upon comparison between the result of measurement stored in the storage device and a result of measurement on the pattern in the region subject to inspection.
(9) The pattern inspecting apparatus as set forth in (1), wherein the detecting optical system includes an imaging device which two-dimensionally images a substantially entire region of the workpiece or a specified region thereof required for inspection.
(10) A pattern inspecting apparatus which inspects a pattern formed on a workpiece to be inspected, said apparatus comprising:
an illuminating optical system having a lamp and a diffusion plate;
a detecting optical system having an imaging lens and an image pickup element, the image pickup element having a certain number of pixels which cannot optically resolve a fine pattern formed on the workpiece to be inspected;
a wavelength-varying system inserted into an optical path extending from the lamp to the image pickup element, the wavelength-varying system having a drive unit;
an image processor operatively connected to the detecting optical system; and
a controller operatively connected to the drive unit and the image processor.
(11) The pattern inspecting apparatus as set forth in (10), wherein the wavelength-varying system varies light of a wide band to light of a narrow band by selectively varying a central wavelength.
(12) The pattern inspecting apparatus as set forth in (10), further comprising:
a storage device which stores therein a result of measurement on a standard workpiece and which is operatively connected to the image processor.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 10-215920 (filed on Jul. 30, 1998), which is expressly incorporated herein by reference in its entirety.